GCSE Computer Science/Fundamentals of computer systems
What is a computer?
You have probably had a lot of experience with computers. They are a type of machine or device which can be programmed. Computers range from the desktop or laptop you are probably reading this on, to a computer in a vending machine or supermarket checkout. Computers are everywhere in out modern life, and are incredibly important to the functioning of the modern world.
The first programmable computer was designed in 1837 by Charles Babbage and Ada Lovelace.
All computer systems work in a similar way. They have inputs, processes and outputs. Take making a phone call on a mobile phone as an example.
|User uses touchscreen to enter the number in||Phone makes contact with towers, and is connected to the other phone||Speaker outputs voice of other person|
Reliability of computer systems
Considering that computers are currently used for so much in the modern world, keeping them running well and constantly is an important consideration. A Crittical system is one which needs to constantly be running, or else there is a risk of death, serious injury, or financial problems.
Why does a life support system need to be reliable? 
In a question like this, you should look at the number of marks, and try to make roughly that number of developed points.
A life support system is a particular type of critical system. A critical system is one which would cause death, serious injury or financial loss if switched off. In the case of a life support system, failure can cause death of the patient. If a life support system was not reliable, it could cause death of a patient. For this reason it will need to be reliable.
Other examples of critical systems include utilities, banking, emergency communications and air traffic control.